August 2016 Issue

Foreign Service

Like many things, there’s more than one way to diagnose Honda evap system problems. As long as the methods are logical and provide reliable results, the more the merrier.

Holy cow, I have more tips on testing purge solenoid valves on Honda evaporative emissions systems. This advice complements the information in the June 2016 Foreign Service column. Here’s the lowdown.

First and foremost, read my June column first if you haven’t done so already. There I described how a failing purge solenoid valve could cause an erroneous leak code on a Honda evap system. The code, P1457, supposedly indicates a canister-side leak in the system. Experience has shown that this bogus leak code is especially common on 2001-05 Civics.

Pinpointing this failing purge valve is potentially pesky because the common checks indicate that it’s working both electrically and mechanically. For example, you can put a stethoscope or screwdriver on the solenoid during purging and hear it clicking steadily. At the same time, a digital meter or scan tool would show that the ECM is steadily pulsing the solenoid on and off. Also, if you teed the proper vacuum gauge into the canister side of the evap system during purging, the gauge would pulse, indicating that the purge solenoid valve was working.

But MOTOR reader Brandon Steckler showed how a scope test could confirm that a purge solenoid really wasn’t working properly after all (refer back to pages 12 and 14 of the June issue for the details). In other words, the purge valve operates but not well enough for the engine to purge the evap system properly during the evap monitor. Due to insufficient purging, the ECM measures weak system vacuum during the evap monitor. Then the ECM concludes that the root cause is a leak on the canister side of the evap system, triggering the P1457 code. In fact, the ECM may set the P1457 repeatedly during the diagnostic process. For example, you may try various fixes and clear the code after each repair. But the bogus P1457 reappears after each attempt.

Denis Kerechuk is the Honda ace at Kerechuk Motor Service in Alhambra, CA. A longtime compadre and Motor reader, he responded to the June column with a method he devised to test suspect purge solenoid valves. He’s seen a lot of Honda vehicles—especially 2001-05 Civics—that arrived with either the P1456 (fuel tank side) or P1457 (canister side) leak codes. As he gained more experience with them, he realized that a marginal purge solenoid valve could be the root cause of the car’s problems. Regardless of which leak code appeared, Kerechuk stopped assuming that the purge solenoid valve was working correctly. He also learned that the familiar checks weren’t pinpointing these marginal purge valves for him. Once again, marginal describes a purge solenoid valve that operates but not well enough for the evap system to pass the monitor.

Fortunately, performing Kerechuk’s procedure is fairly easy. You’ll need a scan tool that communicates effectively with the Honda ECM/PCM as well as a traditional vacuum gauge. By traditional, I mean a gauge that measures 0 to 30 inches of mercury (in.-Hg). Begin by accessing the purge solenoid valve itself. On 2001-05 Civics, this requires removing the air cleaner assembly. Then connect the scan tool and watch the PIDs for coolant temperature and purge solenoid duty cycle. In a pinch, you could monitor purge solenoid duty cycle by connecting a digital meter directly to the purge solenoid itself.

Next, warm up the engine to operating temperature; wait for the ECM/PCM to command the evap purge process. Purging usually begins soon after the engine warms up. Of course, the purge process is underway when you see a duty cycle reading for the purge solenoid on your scanner or digital meter. What’s more, you can hear the purge solenoid clicking steadily. Kerechuk stressed that he’s had the most consistent success with this method when the engine is at operating temperature and purge solenoid duty cycle is about 28% or greater.

Now unplug the purge solenoid valve’s electrical connector while the engine is idling. Then disconnect the hose from the canister side of the purge solenoid valve. Next, connect your vacuum gauge to the open port on the purge solenoid valve. Now the engine will “purge” the vacuum gauge instead of the evap system. Finally, reconnect the electrical connector onto the purge solenoid valve.

Suppose the purge solenoid valve is healthy. In that case, Kerechuk explained, the vacuum gauge needle will rise to manifold vacuum the moment you reconnect the electrical connector to the purge solenoid. No joke here; look for an instantaneous gauge response when you reconnect that solenoid’s harness connector. The gauge needle should zoom right up to manifold vacuum without hesitation. Furthermore, Kerechuk estimated that the gauge needle should react within one-half second of when you reconnect the harness connector.

Interestingly enough, Kerechuk uses a decidedly low-tech way to time the reaction of a suspect Honda purge valve. Although this sounds subjective, he argued that it’s both straightforward and reliable. First, imagine that the engine is idling at operating temperature; you have the vacuum gauge on the canister side of the purge valve and its harness disconnected. Focus on the face of that vacuum gauge; reconnect the harness connector and then say “thousand one” out loud. That’s right—speak those words out loud at a normal pace.

According to Kerechuk, the gauge needle should peak at manifold vacuum by the time you have uttered the word “thousand.” If it does, the purge valve is responding normally. On the other hand, if the gauge needle doesn’t reach manifold vacuum until you have said “thousand one”—or perhaps has taken longer than that—then the purge valve is sluggish.

Okay, I offered a higher-tech diagnostic technique back in June. This time I discussed a simple, low-tech method for testing suspect purge solenoid valves. Hopefully, Kerechuk’s approach will be a worthwhile addition to your troubleshooting notebook. It’s always better to have more troubleshooting choices than fewer.

Believe it or not, this takes me back to the lake shore where we kids used to fish. We would always inspect the bait and tackle that the wiser, older guys used. One of them gave us practical advice:

“There’s more than one way to catch fish, boys. As long as you bring home some fish for dinner, your way is fine,” he said.

Anyway, I can’t reminisce too long. I promised the boss that I’d put my tools away and mop the garage floor this morning—make the place look civilized again. Everyone try to stay cool until September rolls around. I’ll look for you then.